You're going to need some specifics here -- sound systems go up into the hundreds of thousands of dollars.

My advice is to get a good receiver and speakers of the consumer level, and call it a day. That's about $700 when you're all done. The option I would look for is the ability to have more than one set of speakers, or to do 5-speaker surround, so you can add speakers wherever you are lacking.

For example, my primary unit is really good with highs and lows, but needs midrange. At some point, I'll stir my lazy ass and get some midrange speakers for full sound. It's not as important to buy a matched set as to pick speakers that sound good in the ranges you're seeking. Most audio stores and even some Best Buys will let you bring in a sample CD. I use a CD-R that's mostly "Onward to Golgotha"

I got a Sherwood receiver from Radioshack for under $100 that I've had for awhile now, pretty straightforward and no problems. If you have any friends that know audio equipment I recommend going to some thrift stores with them, often you can find really nice speakers with a really good range. If you're not comfortable with the possibility of getting a busted set of speakers though you might want to try a used/refurbished music store. You could probably still walk away from that with a nice sound system for $200-$300. I don't know why but older speakers just sound better to me and the bigger issue is if you want new high quality speakers you could end up spending thousands.

I prefer just using 10 dollar headphones. To my experience "closed" headphones with plastic caps to block outside noises will provide a much more intimate listening experience than any set of speakers. Music sounds more clear and I hear more details. And you can turn up the volume without having to worry about neighbors or flatmates. The 10 dollar headphones I am referring to happen to have very good quality sound for their price but unfortunately they break easily. You might want to get something from the 25-50 dollar range instead, for that price you can get wireless headphones too.

We're all experienced listeners here and pay attention to our music. That's why I would recommend getting a system of at least $1000 value, retail. That doesn't mean you have to spend that much, look for second-hand and discounted items. It's not just about hearing detail, it's the depth and tunefulness (for want of a better word) that a good system gives you. You will also refine your taste - bad music becomes worse and good music becomes better. But first go to a specialist hi-fi store and ask if you can listen to a high quality system - if you can't hear much difference then there's no point spending a lot.

I prefer just using 10 dollar headphones. To my experience "closed" headphones with plastic caps to block outside noises will provide a much more intimate listening experience than any set of speakers. Music sounds more clear and I hear more details. And you can turn up the volume without having to worry about neighbors or flatmates. The 10 dollar headphones I am referring to happen to have very good quality sound for their price but unfortunately they break easily. You might want to get something from the 25-50 dollar range instead, for that price you can get wireless headphones too.

I've noticed there's a huge leap in sound quality and volume at $50 and then again between $100 and $200+ usually based on the brand. It must have to do with the parts they use. For mixing music I have a pair of studio monitor headphones, but the ones I've been buying for years (I usually step on them or something after a couple years) purely for enjoyment are these Sony earbud kind that are around $50. I can't find the exact model anymore but here are their earbud models: http://www.sonystyle.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10551&storeId=10151&langId=-1&categoryId=3727 I highly recommend anything between $50 and $100 there. I don't know about above $100 as I haven't had the opportunity to try any and often they just add on features that don't really make much of a difference.

If this sound system is for music exclusively, ignore 5.1 systems or anything like that. Music is stereo, and should only be represented by 2 speakers and an optional subwoofer. Don't spend under $200, and unless you're made of money, don't spend more than 1k. My advice? Grab a pair of bookshelf speakers. Pick up something like the AudioEngine A5s and forget about it. The audiophile requires a lot of money, patience, and time. And it's not worth worrying about. All you need is a good pair of bookshelf speakers and call it day. Chances are none of the music you listen to is well-produced enough to take advantage of an expensive sound system.

^ If you can swing it, and unless the main speakers are themselves very substantial(particularly low-end wise), I cannot recommend a subwoofer enough. On everything from Brahms to Morbid Angel and back it enhances the listening experience dramatically when you can essentially feel, as well as hear the music!

They certainly would benefit from a quality subwoofer - but they have more than enough low end on their own. Black metal and death metal from my experience benefit least from a subwoofer - and a lot of subwoofers aren't quick enough to accurately replicate double bass.

^ Curious - my subwoofer can handle any double-bass I throw at it and at volume, with full clarity and power reproduced. I will agree that a subwoofer is not likely to do much sonically for say, a Darkthrone or the like.